The problem with the Canon lens is that it is only 0.5x magnification. In order to get it to 1:1 you need to either buy the 1x adapter, extension tubes or close up lenses. The 1x adapter costs almost as much as the lens itself. If you use either the tubes or the adapter you will lose speed (f stops). Depending on how the lens was designed you may lose optical quality with tubes or lenses. You will also lose working distance. You may lose automation (metering, stop down etc.) with the tubes.
Working distance is the distance from the front of the lens to the subject. This is important in macro photography for nature. The more distance the less likely are you to startle living subjects. The more distance you have the more control you have over lighting. It's all about lighting photographers will tell you.